This invention relates to transmission systems handling both circuit switched traffic and packet switched traffic.
Most telephone systems exist to provide a "circuit switched" speech information service, and represent a substantial capital investment. During recent years there has been a rapidly increasing demand for digital data information resulting in additional dedicated networks, both circuit switched and packet switched. In addition, much work has been done to adapt existing telephone networks to carry data traffic.
The development of digital transmission and switching has accelerated this trend by enabling the provision of a completely digital network comprising entirely electronic devices, culminating in the imminent introduction of an ISDN (Integrated Services Digital Network) which provides simultaneous access for telephone and data subscribers on the same circuit.
Frequently independently-operated circuit switched and packet switched networks provide services to subscribers in the same area. System nodes may even be co-located and the duplication of trunk transmission facilities represents an uneconomic use of available capital resources.